The present invention relates to optical apparatuses such as a digital still camera, a video camera and an interchangeable lens, and more particularly relates to an optical apparatus that moves an optical member such as a lens using a lead screw and a rack.
The optical apparatus as stated above has a configuration in which a rack engaging with the lead screw is attached to the holding member holding the optical member. As the lead screw is rotated by a motor, the engagement of the lead screw with a tooth portion of the rack causes the conversion of the rotation force of the lead screw into a driving force in a shaft direction, thus allowing the holding member to move in the optical axis direction.
Japanese Patent Laid-Open No. 8 (1996)-248284 discloses a rack including a first tooth portion and a second tooth portion that sandwich a lead screw therebetween from both sides of a radial direction of the lead screw and engage therewith. The first tooth portion functions as a main rack tooth and the second tooth portion functions as a press portion that presses the first tooth against the lead screw, where the second tooth portion has an apex angle set so as not to contact with the outer diameter portion of the lead screw. Thereby, when the lead screw slides with respect to the press portion, the generation of abnormal noise due to the surface roughness of the outer diameter portion of the lead screw can be prevented. Herein, a tooth formed at each tooth portion has a shape extending in the direction orthogonal to the shaft direction of the lead screw.
Japanese Patent Laid-Open No. 6 (1994)-174992 discloses an optical apparatus including a rack having a first tooth portion and a second tooth portion inclined to the side of a lead screw with reference to the first tooth portion (so that the second tooth portion has a drawing angle), thus preventing the wobble of a holding member (i.e., an optical member) to which the rack is attached.
In the optical apparatus disclosed in Japanese Patent Laid-Open No. 8 (1996)-248284, however, since the tooth formed at each tooth portion of the rack extends in the direction orthogonal to the shaft direction of the lead screw, the sliding resistance thereof is large. In order to reduce such sliding resistance, each tooth may extend in the lead angle direction of the lead screw. That is, the tooth of the first tooth portion and the tooth of the second tooth portion may be formed so that their extending directions cross each other when viewed from the radial direction of the lead screw.
When considering the case where such a rack is integrally formed with resin, however, since the tooth extending direction is different form the removing direction of a die for forming the tooth, it is impossible to remove the die. That is, it is difficult to manufacture the rack because of a limit of the die configuration.
In the optical apparatus disclosed in Japanese Patent Laid-Open No. 6 (1994)-174992, since the second tooth portion has a drawing angle, local stress occurs at the second tooth portion when the die for forming the second tooth portion is removed, so that the second tooth portion may be damaged or broken.